An enhanced video experience can be obtained by overlaying a graphics object on an elementary image, or on a sequence of elementary images that constitute a video. Adding subtitles is a basic example in which the graphics objects is in the form of text. In more advanced applications, one or more graphics object may represent a drawing, which may have a conceptual relationship with the elementary image. It is also possible to add an animation to a video based on one or more graphics objects.
A standard has been developed for so-called Blu-ray Disc applications, which are capable of providing enhanced video experiences. The standard specifies so-called graphics object segments, which provides a basic representation of a graphics object in an encoded form. The standard further specifies so-called composition segments. A composition segment describes a given appearance of a graphics object to which the composition segment relates. The basic representation of the graphics object needs to be processed in order to achieve this given appearance. This processing may include operations, such as, for example, cropping, positioning, color mapping. A graphics controller typically defines these operations on the basis of the composition segment concerned. The graphics object that results from processing the basic representation thereof is typically placed in a so-called graphics plane. This graphics plane is then overlaid on a video plane, which corresponds with an image of a video. The video plane can thus be regarded as an elementary image onto which the graphics object is overlaid.
United States patent application published under number US 2006/0294543 describes background art techniques according to which a reproduction apparatus separately decodes a video stream and a graphics stream and overlays resulting video and graphics to produce a reproduction image. The graphics stream is an arrangement of so-called PES packets, and these packets can be classified into two types: PES packets carrying control information and PES packets carrying graphics data, which represents graphics. One pair of control information and graphics data produces one graphics display. The reproduction apparatus reads the control information and the graphics data in sequence, decodes the control information, and also decodes the graphics data to generate uncompressed graphics. The reproduction apparatus displays the uncompressed graphics with a desired presentation timing, according to a decoding result of the control information